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David A Penning - One of the best experts on this subject based on the ideXlab platform.
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the scaling of terrestrial striking performance in western ratsnakes Pantherophis obsoletus
Journal of Experimental Zoology, 2020Co-Authors: David A Penning, Baxter Sawvel, Brad R MoonAbstract:: In many organisms, juveniles have performance capabilities that partly offset their disadvantageous sizes. Using high-speed video recordings and imaging software, we measured the scaling of head morphology, axial morphology, and defensive strike performance of Pantherophis obsoletus across their ontogeny to understand how size and morphology affect performance. Head measurements were negatively allometric whereas the cross-sectional area (CSA) of epaxial muscles displayed positive allometry. The greater relative muscle CSA of larger ratsnakes allows them to produce higher forces relative to their mass, and those forces act on a relatively smaller head mass when it is thrust forward during striking. Maximum strike accelerations of 70-273.8 ms-2 and velocities of 1.08-3.39 ms-1 scaled positively with body mass but differed from the geometric predictions. Velocity scaled with mass0.15 and acceleration scaled with mass0.17 . Larger snakes struck from greater distances (range = 4.1-26 cm), but all snakes covered the strike distances with similarly short durations (84 ± 3 ms). The negatively allometric head size, isometry of anterior mass, and positively allometric muscle CSA enable larger P. obsoletus to strike with higher velocities and accelerations than smaller individuals. Our results contrast with the scaling of strike performance in an arboreal viper, whose strike distance and velocity were independent of body mass. When strike distance is modulated, all other performance capacities are affected because of the interdependence of acceleration, velocity, duration, and distance.
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quantitative axial myology in two constricting snakes lampropeltis holbrooki and Pantherophis obsoletus
Journal of Anatomy, 2018Co-Authors: David A PenningAbstract:: A snake's body represents an extreme degree of elongation with immense muscle complexity. Snakes have approximately 25 different muscles on each side of the body at each vertebra. These muscles serially repeat, overlap, interconnect, and rarely insert parallel to the vertebral column. The angled muscles mean that simple measurements of anatomical cross-sectional area (ACSA, perpendicular to the long-axis of the body) serve only as proxies for the primary determinant of muscle force, physiological cross-sectional area (PCSA, area perpendicular to the muscle fibers). Here, I describe and quantify the musculature of two intraguild constrictors: kingsnakes (Lampropeltis holbrooki) and ratsnakes (Pantherophis obsoletus) whose predation performance varies considerably. Kingsnakes can produce significantly higher constriction pressures compared with ratsnakes of similar size. In both snakes, I provide qualitative descriptions, detail previously undescribed complexity, identify a new lateral muscle, and provide some of the first quantitative measures of individual muscle and whole-body PCSA. Furthermore, I compare measurements of ACSA with measurements of PCSA. There was no significant difference in PCSA of muscles between kingsnakes and ratsnakes. There is, however, a strong relationship between ACSA and PCSA measurements. I could not identify a significant difference in musculature between kingsnakes and ratsnakes that explains their different levels of constriction performance. Unmeasured components of muscle function, such as endurance and force production, might account for differences in performance between two species with similar muscle structure.
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the king of snakes performance and morphology of intraguild predators lampropeltis and their prey Pantherophis
The Journal of Experimental Biology, 2017Co-Authors: David A Penning, Brad R MoonAbstract:ABSTRACT Across ecosystems and trophic levels, predators are usually larger than their prey, and when trophic morphology converges, predators typically avoid predation on intraguild competitors unless the prey is notably smaller in size. However, a currently unexplained exception occurs in kingsnakes in the genus Lampropeltis . Kingsnakes are able to capture, constrict and consume other snakes that are not only larger than themselves but that are also powerful constrictors (such as ratsnakes in the genus Pantherophis ). Their mechanisms of success as intraguild predators on other constrictors remain unknown. To begin addressing these mechanisms, we studied the scaling of muscle cross-sectional area, pulling force and constriction pressure across the ontogeny of six species of snakes ( Lampropeltis californiae , L. getula , L. holbrooki , Pantherophis alleghaniensis , P. guttatus and P. obsoletus ). Muscle cross-sectional area is an indicator of potential force production, pulling force is an indicator of escape performance, and constriction pressure is a measure of prey-handling performance. Muscle cross-sectional area scaled similarly for all snakes, and there was no significant difference in maximum pulling force among species. However, kingsnakes exerted significantly higher pressures on their prey than ratsnakes. The similar escape performance among species indicates that kingsnakes win in predatory encounters because of their superior constriction performance, not because ratsnakes have inferior escape performance. The superior constriction performance by kingsnakes results from their consistent and distinctive coil posture and perhaps from additional aspects of muscle structure and function that need to be tested in future research.
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prey handling behaviors of naive Pantherophis guttatus
Journal of Herpetology, 2016Co-Authors: David A Penning, Stefan CairnsAbstract:Abstract We studied the effects of relative prey mass and experience on prey-handling behaviors of 16 ingestively naive Corn Snakes (Pantherophis guttatus) feeding on different categorical sizes of live House Mice (Mus musculus) over 11 feeding trials. We randomly assigned hatchlings to two categories of prey mass, relative to snake mass (small = 20–40% and large = 41–60%), and analyzed the effects of prey mass on capture position, prey-handling method, time to subdue prey, condition of prey at ingestion, direction of ingestion, and duration of ingestion. Prey mass significantly affected prey-handling behaviors. As snakes experienced larger prey, they used more complex prey-handling behaviors (hairpin loops and constriction). Snakes that had prior large-prey experience maintained constant subduing times across feeding trials, whereas snakes that had prior experience with small prey showed an increase in subduing time across trials. Snakes feeding on large prey took longer to ingest prey than snakes feedin...
Edward A Myers - One of the best experts on this subject based on the ideXlab platform.
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resolving spatial complexities of hybridization in the context of the gray zone of speciation in north american ratsnakes Pantherophis obsoletus complex
bioRxiv, 2020Co-Authors: Frank T. Burbrink, Marcelo Gehara, Edward A MyersAbstract:Estimating species divergence with gene flow has been crucial for characterizing the gray zone of speciation, which is the period of time where lineages have diverged but have not yet achieved strict reproductive isolation. However, estimates of divergence times and gene flow often ignores spatial information, for example the formation and shape of hybrid zones. Using population genomic data from the eastern ratsnake complex (Pantherophis obsoletus), we infer phylogeographic groups, gene flow, changes in demography, the timing of divergence, and hybrid zone widths. We examine the spatial context of diversification by linking migration and timing of divergence to the size, shape, and types of hybridization (e.g., F1, backcrosses) in hybrid zones. Rates of migration between lineages are associated with the width and shape of hybrid zones. Timing of divergence is not related to migration rate across species pairs and is therefore a poor proxy for inferring position in the gray zone. Artificial neural network approaches are applied to understand how landscape features and past climate have influenced population genetic structure among these lineages prior to hybridization. The Mississippi River produced the deepest divergence in this complex, whereas Pleistocene climate and elevation secondarily structured lineages.
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Biogeographic barriers, Pleistocene refugia, and climatic gradients in the southeastern Nearctic drive diversification in cornsnakes (Pantherophis guttatus complex).
Molecular Ecology, 2020Co-Authors: Edward A Myers, Alexander D. Mckelvy, Frank T. BurbrinkAbstract:: The southeastern Nearctic is a biodiversity hotspot that is also rich in cryptic species. Numerous hypotheses (e.g., vicariance, local adaptation, and Pleistocene speciation in glacial refugia) have been tested in an attempt to explain diversification and the observed pattern of extant biodiversity. However, previous phylogeographic studies have both supported and refuted these hypotheses. Therefore, while data support one or more of these diversification hypotheses, it is likely that taxa are forming within this region in species-specific ways. Here, we generate a genomic data set for the cornsnakes (Pantherophis guttatus complex), which are widespread across this region, spanning both biogeographic barriers and climatic gradients. We use phylogeographic model selection combined with hindcast ecological niche models to determine regions of habitat stability through time. This combined approach suggests that numerous drivers of population differentiation explain the current diversity of this group of snakes. The Mississippi River caused initial speciation in this species complex, with more recent divergence events linked to adaptations to ecological heterogeneity and allopatric Pleistocene refugia. Lastly, we discuss the taxonomy of this group and suggest there may be additional cryptic species in need of formal recognition.
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biogeographic barriers pleistocene refugia and climatic gradients in the southeastern nearctic drive diversification in cornsnakes Pantherophis guttatus complex
Molecular Ecology, 2020Co-Authors: Alexander D. Mckelvy, Edward A Myers, Frank T. BurbrinkAbstract:: The southeastern Nearctic is a biodiversity hotspot that is also rich in cryptic species. Numerous hypotheses (e.g., vicariance, local adaptation, and Pleistocene speciation in glacial refugia) have been tested in an attempt to explain diversification and the observed pattern of extant biodiversity. However, previous phylogeographic studies have both supported and refuted these hypotheses. Therefore, while data support one or more of these diversification hypotheses, it is likely that taxa are forming within this region in species-specific ways. Here we generate a genomic dataset for the cornsnakes (P. guttatus complex), which are widespread across this region, spanning both biogeographic barriers and climatic gradients. We use phylogeographic model selection combined with hindcast ecological niche models to determine regions of habitat stability through time. This combined approach suggests that numerous drivers of population differentiation explain the current diversity of this group of snakes. The Mississippi River caused initial speciation in this species complex, with more recent divergence events linked to adaptations to ecological heterogeneity and allopatric Pleistocene refugia. Lastly, we discuss the taxonomy of this group and suggest there may be additional cryptic species in need of formal recognition.
Jinelle H. Sperry - One of the best experts on this subject based on the ideXlab platform.
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geographic variation in body size and sexual size dimorphism of north american ratsnakes Pantherophis spp s l
Canadian Journal of Zoology, 2018Co-Authors: Brett A Degregorio, Gabriel Blouindemers, Jinelle H. Sperry, Gerardo L F Carfagno, Whitfield J Gibbons, Stephen J Mullin, John D Willson, Kenny WrayAbstract:Because body size affects nearly all facets of an organism’s life history, ecologists have long been interested in large-scale patterns of body-size variation, as well as why those large-scale patterns often differ between sexes. We explored body-size variation across the range of the sexually dimorphic Ratsnake complex (species of the genus Pantherophis Fitzinger, 1843 s.l.; formerly Elaphe obsoleta (Say in James, 1823)) in North America. We specifically explored whether variation in body size followed latitudinal patterns or varied with climatic variables. We found that body size did not conform to a climatic or latitudinal gradient, but instead, some of the populations with the largest snakes occurred near the core of the geographic range and some with the smallest occurred near the northern, western, and southern peripheries of the range. Males averaged 14% larger than females, although the degree of sexual size dimorphism varied between populations (range: 2%–25%). There was a weak trend for male bod...
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do seasonal patterns of rat snake Pantherophis obsoletus and black racer coluber constrictor activity predict avian nest predation
Ecology and Evolution, 2016Co-Authors: Jinelle H. Sperry, Michael P. Ward, Brett A DegregorioAbstract:Avian nest success often varies seasonally and because predation is the primary cause of nest failure, seasonal variation in predator activity has been hypothesized to explain seasonal variation in nest success. Despite the fact that nest predator communities are often diverse, recent evidence from studies of snakes that are nest predators has lent some support to the link between snake activity and nest predation. However, the strength of the relationship has varied among studies. Explaining this variation is difficult, because none of these studies directly identified nest predators, the link between predator activity and nest survival was inferred. To address this knowledge gap, we examined seasonal variation in daily survival rates of 463 bird nests (of 17 bird species) and used cameras to document predator identity at 137 nests. We simultaneously quantified seasonal activity patterns of two local snake species (N = 30 individuals) using manual (2136 snake locations) and automated (89,165 movements detected) radiotelemetry. Rat snakes (Pantherophis obsoletus), the dominant snake predator at the site (~28% of observed nest predations), were most active in late May and early June, a pattern reported elsewhere for this species. When analyzing all monitored nests, we found no link between nest predation and seasonal activity of rat snakes. When analyzing only nests with known predator identities (filmed nests), however, we found that rat snakes were more likely to prey on nests during periods when they were moving the greatest distances. Similarly, analyses of all monitored nests indicated that nest survival was not linked to racer activity patterns, but racer‐specific predation (N = 17 nests) of filmed nests was higher when racers were moving the greatest distances. Our results suggest that the activity of predators may be associated with higher predation rates by those predators, but that those effects can be difficult to detect when nest predator communities are diverse and predator identities are not known. Additionally, our results suggest that hand‐tracking of snakes provides a reliable indicator of predator activity that may be more indicative of foraging behavior than movement frequency provided by automated telemetry systems.
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Evaluation of Automated Radio Telemetry for Quantifying Movements and Home Ranges of Snakes
Journal of Herpetology, 2013Co-Authors: Michael P. Ward, Jinelle H. SperryAbstract:Abstract We evaluated an automated telemetry system that can dramatically increase the amount of activity and spatial data collected for snakes. We developed methods for analyzing data from single automated receiving units (ARUs) and ARU arrays, compared results from ARUs with conventional hand tracking, and assessed previously untested assumptions used in conventional telemetry, using data from ratsnakes (Pantherophis spp.) in Texas and Illinois. ARU data indicated that ratsnakes spent most of their time in small home ranges (mean = 25 ha) but engaged in forays of up to 1.5 km from their core-use areas, suggesting this species may engage in central place foraging. Forays inflated home-range sizes greatly if areas were estimated using minimum convex polygons rather than 95% kernels. Large numbers of locations generated by ARUs produce more reliable home-range estimates than those from hand tracking. ARU data indicated that snakes moved in response to observers during hand tracking. Daily hand tracking pro...
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Effects of Temperature, Moon Phase, and Prey on Nocturnal Activity in Ratsnakes: An Automated Telemetry Study
Journal of Herpetology, 2013Co-Authors: Jinelle H. Sperry, Michael P. WardAbstract:Abstract Nocturnal activity is important for many animals, but difficulty in documenting that activity has hampered efforts to understand factors that influence when animals are active at night. We used automated radiotelemetry to provide the first detailed tests of the hypothesis that the nocturnal activity of free-ranging snakes should be influenced by temperature, moon phase, and prey abundance by using data for Ratsnakes (Pantherophis spp.) from Texas and Illinois. Ratsnakes exhibited some nocturnal behavior throughout their active season in both Texas and Illinois, although snakes were much more active at night in Texas than in Illinois. Texas snakes transitioned from primarily diurnal activity to primarily nocturnal activity over this snake's active season, whereas Illinois snakes were always most active in the middle of the day. For both populations, nocturnal activity was positively related to temperature but unrelated to moon phase. Ratsnakes in Texas exhibited a stepwise increase in nocturnal ac...
Frank T. Burbrink - One of the best experts on this subject based on the ideXlab platform.
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resolving spatial complexities of hybridization in the context of the gray zone of speciation in north american ratsnakes Pantherophis obsoletus complex
bioRxiv, 2020Co-Authors: Frank T. Burbrink, Marcelo Gehara, Edward A MyersAbstract:Estimating species divergence with gene flow has been crucial for characterizing the gray zone of speciation, which is the period of time where lineages have diverged but have not yet achieved strict reproductive isolation. However, estimates of divergence times and gene flow often ignores spatial information, for example the formation and shape of hybrid zones. Using population genomic data from the eastern ratsnake complex (Pantherophis obsoletus), we infer phylogeographic groups, gene flow, changes in demography, the timing of divergence, and hybrid zone widths. We examine the spatial context of diversification by linking migration and timing of divergence to the size, shape, and types of hybridization (e.g., F1, backcrosses) in hybrid zones. Rates of migration between lineages are associated with the width and shape of hybrid zones. Timing of divergence is not related to migration rate across species pairs and is therefore a poor proxy for inferring position in the gray zone. Artificial neural network approaches are applied to understand how landscape features and past climate have influenced population genetic structure among these lineages prior to hybridization. The Mississippi River produced the deepest divergence in this complex, whereas Pleistocene climate and elevation secondarily structured lineages.
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Biogeographic barriers, Pleistocene refugia, and climatic gradients in the southeastern Nearctic drive diversification in cornsnakes (Pantherophis guttatus complex).
Molecular Ecology, 2020Co-Authors: Edward A Myers, Alexander D. Mckelvy, Frank T. BurbrinkAbstract:: The southeastern Nearctic is a biodiversity hotspot that is also rich in cryptic species. Numerous hypotheses (e.g., vicariance, local adaptation, and Pleistocene speciation in glacial refugia) have been tested in an attempt to explain diversification and the observed pattern of extant biodiversity. However, previous phylogeographic studies have both supported and refuted these hypotheses. Therefore, while data support one or more of these diversification hypotheses, it is likely that taxa are forming within this region in species-specific ways. Here, we generate a genomic data set for the cornsnakes (Pantherophis guttatus complex), which are widespread across this region, spanning both biogeographic barriers and climatic gradients. We use phylogeographic model selection combined with hindcast ecological niche models to determine regions of habitat stability through time. This combined approach suggests that numerous drivers of population differentiation explain the current diversity of this group of snakes. The Mississippi River caused initial speciation in this species complex, with more recent divergence events linked to adaptations to ecological heterogeneity and allopatric Pleistocene refugia. Lastly, we discuss the taxonomy of this group and suggest there may be additional cryptic species in need of formal recognition.
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biogeographic barriers pleistocene refugia and climatic gradients in the southeastern nearctic drive diversification in cornsnakes Pantherophis guttatus complex
Molecular Ecology, 2020Co-Authors: Alexander D. Mckelvy, Edward A Myers, Frank T. BurbrinkAbstract:: The southeastern Nearctic is a biodiversity hotspot that is also rich in cryptic species. Numerous hypotheses (e.g., vicariance, local adaptation, and Pleistocene speciation in glacial refugia) have been tested in an attempt to explain diversification and the observed pattern of extant biodiversity. However, previous phylogeographic studies have both supported and refuted these hypotheses. Therefore, while data support one or more of these diversification hypotheses, it is likely that taxa are forming within this region in species-specific ways. Here we generate a genomic dataset for the cornsnakes (P. guttatus complex), which are widespread across this region, spanning both biogeographic barriers and climatic gradients. We use phylogeographic model selection combined with hindcast ecological niche models to determine regions of habitat stability through time. This combined approach suggests that numerous drivers of population differentiation explain the current diversity of this group of snakes. The Mississippi River caused initial speciation in this species complex, with more recent divergence events linked to adaptations to ecological heterogeneity and allopatric Pleistocene refugia. Lastly, we discuss the taxonomy of this group and suggest there may be additional cryptic species in need of formal recognition.
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Comparative mitochondrial genomics of snakes: extraordinary substitution rate dynamics and functionality of the duplicate control region.
BMC Evolutionary Biology, 2007Co-Authors: Zhi J. Jiang, Todd A. Castoe, Christopher C. Austin, Frank T. Burbrink, Matthew D. Herron, Jimmy A. Mcguire, Christopher L. Parkinson, David D. PollockAbstract:Background The mitochondrial genomes of snakes are characterized by an overall evolutionary rate that appears to be one of the most accelerated among vertebrates. They also possess other unusual features, including short tRNAs and other genes, and a duplicated control region that has been stably maintained since it originated more than 70 million years ago. Here, we provide a detailed analysis of evolutionary dynamics in snake mitochondrial genomes to better understand the basis of these extreme characteristics, and to explore the relationship between mitochondrial genome molecular evolution, genome architecture, and molecular function. We sequenced complete mitochondrial genomes from Slowinski's corn snake (Pantherophis slowinskii) and two cottonmouths (Agkistrodon piscivorus) to complement previously existing mitochondrial genomes, and to provide an improved comparative view of how genome architecture affects molecular evolution at contrasting levels of divergence.
Daniel G Blackburn - One of the best experts on this subject based on the ideXlab platform.
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A Novel Pattern of Yolk Processing in Developing Snake Eggs (Colubridae: Lampropeltini) and its Functional and Evolutionary Implications
Journal of Experimental Zoology, 2017Co-Authors: Kathryn G Powers, Daniel G BlackburnAbstract:Early amniotic vertebrates evolved large-yolked eggs that permitted production of well-developed, terrestrial hatchlings. This reproductive pattern required new mechanisms for cellularizing the yolk and mobilizing it for embryonic use. In birds, cells that line the yolk sac cavity phagocytose and digest the yolk material, a pattern that is commonly assumed to be universal among oviparous amniotes. However, recent evidence challenges the assumption that all squamate reptiles conform to the avian developmental pattern. In this paper, scanning electron microscopy and histology were used to study mechanisms of yolk processing in two colubrid snakes, the kingsnake Lampropeltis getula and the milksnake L. triangulum. Endodermal cells from the yolk sac splanchnopleure proliferate massively as they invade the yolk sac cavity, forming elaborate chains of interlinked cells. These cells grow in size as they phagocytose yolk material. Subsequently, vitelline capillaries invade the masses of yolk-laden cells and become coated with the endodermal cells, forming an elaborate meshwork of cell-coated strands. The close association of cells, yolk, and blood vessels allows yolk material to be cellularized, digested, and transported for embryonic use. The overall pattern is like that of the corn snake Pantherophis guttatus, but contrasts markedly with that of birds. Given recent evidence that this developmental pattern may also occur in certain lizards, we postulate that it is ancestral for squamates. Studies of lizards, crocodilians, and turtles are needed to clarify the evolutionary history of this pattern and its implications for the evolution of the amniotic (terrestrial) vertebrate egg.
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morphological specializations of the yolk sac for yolk processing in embryonic corn snakes Pantherophis guttatus colubridae
Journal of Morphology, 2017Co-Authors: Kathryn G Powers, Daniel G BlackburnAbstract:: Non-avian reptiles commonly are assumed to be like birds in their overall patterns of development. However, colubrid corn snakes (Pantherophis guttatus) have mechanisms of yolk cellularization and processing that are entirely different from the avian pattern. In birds, a vascular "yolk sac" surrounds and digests the liquid yolk. In contrast, in corn snakes, the yolk material is converted into vascularized cords of yolk-filled cells. In this study, we used stereomicroscopy, histology, and scanning electron microscopy to analyze this unusual developmental pattern in corn snakes. Our observations reveal that the yolk sac cavity is invaded by endodermal cells that proliferate, absorb yolk spheres, and form aggregates of interconnected cells within the liquid yolk mass. As development proceeds, small blood vessels arise from the yolk sac omphalopleure, penetrate into the yolk mass, and become tightly encased in the endodermal cells. The entire vitellus ultimately becomes converted into a mass of vascularized, "spaghetti-like" strands of yolk-laden cells. The resulting arrangement allows yolk to be digested intracellularly and yolk products to be transported to the developing embryo. Indirect evidence for this pattern in other species raises the possibility that it is ancestral for squamates and quite possibly Reptilia in general.
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Ultrastructure of the fetal membranes of the oviparous kingsnake, Lampropeltis getula (Colubridae) as revealed by scanning electron microscopy
Journal of Morphology, 2015Co-Authors: Daniel G BlackburnAbstract:In reptilian sauropsids, fetal (extraembryonic) membranes that line the eggshell sustain developing embryos by providing for gas exchange and uptake of water and eggshell calcium. However, a scarcity of morphological studies hinders an understanding of functional specializations and their evolution. In kingsnakes (Lampropeltis getula), scanning electron microscopy reveals two major fetal membranes: the chorioallantois and yolk sac omphalopleure. In early development, the chorioallantois contains tall chorionic epithelial cells, avascular connective tissue, and enlarged allantoic epithelial cells. During its maturation, the chorionic and allantoic epithelia thin dramatically and become underlain by a rich network of allantoic capillaries, yielding a membrane ideally suited for respiratory gas exchange. Yolk sac development initially is like that of typical lizards and snakes, forming an avascular omphalopleure, isolated yolk mass (IYM), and yolk cleft. However, unlike the situation in most squamates studied, the omphalopleure becomes transformed into a “secondary chorioallantois” via three asynchronous events: flattening of the epithelium, regression of the IYM, and vascularization by the allantois. Progressive expansion of chorioallantois parallels growing embryonic needs for gas exchange. In early through mid-development, external surfaces of both the chorionic and omphalopleure epithelium show an abundance of irregular surface protrusions that possibly increase surface area for water absorption. We postulate that the hypertrophied allantoic epithelial cells produce allantoic fluid, a viscous substance that facilitates water uptake and storage. Our findings are consistent with a previous study on the corn snake Pantherophis guttatus, but include new observations and novel functional hypotheses relevant to a reconstruction of basal squamate patterns. J. Morphol. 276:1467–1481, 2015. © 2015 Wiley Periodicals, Inc.
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sources and timing of calcium mobilization during embryonic development of the corn snake Pantherophis guttatus
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2004Co-Authors: James R. Stewart, Tom W Ecay, Daniel G BlackburnAbstract:Embryos of oviparous Reptilia (=turtles, lepidosaurs, crocodilians and birds) extract calcium for growth and development from reserves in the yolk and eggshell. Yolk provides most of the calcium to embryos of lizards and snakes. In contrast, the eggshell supplies most of the calcium for embryonic development of turtles, crocodilians and birds. The yolk sac and chorioallantoic membrane of birds recover and transport calcium from the yolk and eggshell and homologous membranes of squamates (lizards and snakes) probably transport calcium from these two sources as well. We studied calcium mobilization by embryos of the snake Pantherophis guttatus during the interval of greatest embryonic growth and found that the pattern of calcium transfer was similar to other snakes. Calcium recovery from the yolk is relatively low until the penultimate embryonic stage. Calcium removal from the eggshell begins during the same embryonic stage and total eggshell calcium drops in each of the final 2 weeks prior to hatching. The eggshell supplies 28% of the calcium of hatchlings. The timing of calcium transport from the yolk and eggshell is coincident with the timing of growth of the yolk sac and chorioallantoic membrane and expression of the calcium binding protein, calbindin-D28K, in these tissues as reported in previous studies. In the context of earlier work, our findings suggest that the timing and mechanism of calcium transport from the yolk sac of P. guttatus is similar to birds, but that both the timing and mechanism of calcium transport by the chorioallantoic membrane differs. Based on the coincident timing of eggshell calcium loss and embryonic calcium accumulation, we also conclude that recovery of eggshell calcium in P. guttatus is regulated by the embryo.
